The objective of the proposed research is to study by histochemical means the mechanism whereby the motor nerves control the energy metabolism and the myosin ATPase activity of the fibers of white (fast) and red (slow) skeletal muscle. The experiments proposed combine a variety of techniques such as chronic electrical stimulation using implanted stimulators or just implanted electrodes, chronic nerve block, cross-union of nerves, transient denervation, and persistent denervation. An attempt will be made to reverse the preferential energy metabolism and the myosin ATPase activity of the muscle fibers by altering the patterns of electrical stimulation without changing the nerve supply. The experiments are designed in such a manner as to distinguish the role played by different patterns of activity imposed on muscle, from other trophic influences and to gather evidence in favor or against the existence of trophic substances released by the nerve.